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<p>Nearly vertically emitted second-harmonic generation (VESHG) is first demonstrated in an on-chip dispersion-engineered lithium niobate microdisk under unidirectional laser pumping. Leveraging the slight geometric deformation and ultrahigh-Q factors of 3.3×10<sup>6</sup>, strong Rayleigh backscattering and high efficiency nonlinear conversion are demonstrated. Under continuous-wave unidirectional laser pumping at 1556 nm, bidirectional stimulated Raman scattering (SRS) signals at 1620 nm are excited within the microdisk. These bidirectional SRS signals spontaneously form dynamic subwavelength photorefractive gratings (SPGs), providing additional optical momentum (<i>K</i> ≈ 2<i>π</i>/Λ, where Λ is the grating period) to enable phase-matching for VESHG. Experimental results demonstrate successful generation of VESHG at 778 nm with a high absolute conversion efficiency of 0.05% at a pump power of 1.5 mW, achieved without requiring two external counterpropagating pump lasers. This work holds significant potential in various applications in nonlinear frequency conversion, terahertz photonics, optical communication, and quantum technologies that interface free space and photonic integrated circuits.</p>

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Vertically emitted second-harmonic generation in on-chip lithium niobate microdisks under unidirectional laser pumping

  • 期刊论文

  • 发表日期：

    2026年6月24日

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  • Qifeng Hou,
  • Renhong Gao,
  • Chuntao Li,
  • Yingnuo Qiu,
  • Yixuan Yang,
  • Xiaochao Luo,
  • Ni Yao,
  • Min Wang,
  • Jintian Lin,
  • Ya Cheng

摘要

Nearly vertically emitted second-harmonic generation (VESHG) is first demonstrated in an on-chip dispersion-engineered lithium niobate microdisk under unidirectional laser pumping. Leveraging the slight geometric deformation and ultrahigh-Q factors of 3.3×106, strong Rayleigh backscattering and high efficiency nonlinear conversion are demonstrated. Under continuous-wave unidirectional laser pumping at 1556 nm, bidirectional stimulated Raman scattering (SRS) signals at 1620 nm are excited within the microdisk. These bidirectional SRS signals spontaneously form dynamic subwavelength photorefractive gratings (SPGs), providing additional optical momentum (K ≈ 2π/Λ, where Λ is the grating period) to enable phase-matching for VESHG. Experimental results demonstrate successful generation of VESHG at 778 nm with a high absolute conversion efficiency of 0.05% at a pump power of 1.5 mW, achieved without requiring two external counterpropagating pump lasers. This work holds significant potential in various applications in nonlinear frequency conversion, terahertz photonics, optical communication, and quantum technologies that interface free space and photonic integrated circuits.